1. Field of the Invention
This invention relates generally to the formation of an article prototype or model from a mathematical description and more particularly to a system for generating the shape of an article by irradiating successive sheets which comprise a matrix which supports the article during formation.
2. Background Art
Since the implementation of computer technology for physical design purposes, the need for expanding use of computers to control the fabrication of prototypes of articles which have been designed has been appreciated. While the principle of irradiating an article to effect changes in molecular structure and physical properties has been long recognized, such phenomenon had not been employed for the purpose of generating three-dimensional articles until recent years. In this regard, attempts have been made to utilize a fluid medium containing a curable material which was irradiated by a plurality of beams. The energy level at the intersection of the beams was sufficient to cure the material within the fluid medium. Such apparatus did not gain widespread acceptance due to many inherent disadvantages including cost, resolution difficulties and insufficient energy levels as a result of absorption as the depth of beam penetration into the fluid medium increased.
In patent 4,575,330, an apparatus for constructing an article by ultra violet irradiation of the upper surface of a photopolymeric fluid medium was disclosed. Successive layers of an article were generated by lowering each polymerized layer into the fluid medium so that the upper surface of the fluid medium contained unpolymerized material suitable for polymerization and generation of the next layer.
While the apparatus did not require multiple beams, it suffered from several disadvantages. It was limited to use with ultra violet beams and required photopolymers responsive to the ultra violet wavelengths. In addition, difficulties were encountered in maintaining the upper surface of the fluid medium at a planar reference level due to fluid turbulence, reduction in fluid level as a result of the polymerization of prior layers and uneven shrinkage of the polymerized material. Also, the apparatus lacked precise control over the depth of polymerization into the fluid medium which resulted in loss of axial resolution.
Further, because a fluid medium was used, the article being constructed could not be supported by the fluid medium and a support platform, moveable within the medium was required. As such, articles having surfaces contoured with undercuts and the like could not be generated without providing a complicated mechanism capable of moving the platform along multiple axes.